Furnace carrier and handling system

ABSTRACT

In an impurity treatment chamber, such as a gas diffusion furnace or the like, of a type having means for passing gases into and out of a chamber for treating semiconductor elements disposed therein, a carrier is movable longitudinally thereof and adapted to support semiconductor elements within the chamber. An elongated screw mounted for rotation within the chamber adjacent to the bottom thereof cooperates with a follower portion formed on the carrier for engaging the threads of the screw for positive movement of the carrier in response to rotation of the screw. Motive means rotate the screw so as to positively drive the carrier between advanced and retracted positions within the chamber and to oscillate the carrier within the chamber over a short distance so as to preclude adhesion or sticking of the parts of the system which would otherwise make difficult the withdrawal of the carrier from the chamber.

United States Patent [19] Way FURNACE CARRIER AND HANDLING SYSTEMInventor: James A. Way, Mountain View,

Calif.

Assignee: ILL. Schoger & Associates, Inc.,

Santa Clara, Calif.

Filed: Feb. 29, 1972 Appl. No.: 230,500

Related US. Application Data SQUARE WAVE l osc.

T2 L R 68 1 T T STEPPER DRIVER Bl-DIRECTlONAL) PHASE REVERSING 1 May 29,1973 3,215,420 11/1950 Bottenhom ..263/6 R Primary Examiner-John J.Camby Assistant Examiner-Henry C. Yuen Attorney-Flehr, Hohbach, Test,Albritton & Herbert [5 7] ABSTRACT In an impurity treatment chamber,such as a gas diffusion furnace or the like, of a type having means forpassing gases into and out of a chamber for treating semiconductorelements disposed therein, a carrier is movable longitudinally thereofand adapted to support semiconductor elements within the chamber. Anelongated screw mounted for rotation within the chamber adjacent to thebottom thereof cooperates with a follower portion formed on the carrierfor engaging the threads of the screw for positive movement of thecarrier in response to rotation of the screw. Motive means rotate thescrew so as to positively drive the carrier between advanced andretracted positions within the chamber and to oscillate the carrierwithin the chamber over a short distance so as to preclude adhesion orsticking of the parts of the system which would otherwise make difficultthe withdrawal of the carrier from the chamber.

7 Claims, 8 Drawing Figures Patented May 29, 1973 2 Sheets-Sheet 1SQUARE WAVE 080.

G A K 1 E LT R j 7 T W O E E RD 8 INVENTOR. JAMES A WAY ATTORNEYSFURNACE CARRIER AND HANDLING SYSTEM This is a continuation ofapplication Ser. No. 101,036 filed Dec. 23, 1970, now abandoned.

BACKGROUND OF THE INVENTION This invention pertains to impuritytreatment apparatus, for example, of the type used in treatingsemiconductor elements, such as integrated circuits and the like by gasdeposition, gas diffusion, epitaxial growth of semiconductor materials,etc., as conducted in a furnace or reactor chamber.

In a typical diffusion furnace, for example, an elongated, hollowchamber, preferably of quartz material, is disposed in the heating zoneof the furnace or reactor. Semiconductor or other elements to be treatedmay be moved into and out of the heating zone by means of an elongatedcarrier or boat" movable by manipulation applied from an access openingof the chamber.

In operation, the chamber may be sealed at the ac cess opening and gas,such as boron, phosphorous, arsenic, antimony, or others, for treatingthe semiconductor material is passed into and out of the chamber whilethe semiconductor elements are exposed to the gas. After such exposure,the carrier is drawn out of the heating zone and into a cooling zoneoutside the furnace but within the chamber. Ultimately, the carrier isremoved from the chamber entirely to retrieve the treated semiconductorelements.

As has been experienced, movement of the carrier along the surface ofthe tubular chamber frequently is rendered difficult, if not impossible,by adhesion of the carrier to the chamber as a result of bondingdeposits of the treatment gases and otherwise, such as by flaking of anuncured chamber.

SUMMARY OF THE INVENTION AND OBJECTS In general, there is provided afurnace for preparing semiconductor elements in exposure to gasescomprising an elongated chamber or tube carried by the furnace toreceive the elements via an end thereof. Means forming a carrier tosupport a number of the semiconductor elements therefrom in the chambermoves longitudinally of the chamber. An elongated screw ele- 1 ment ismounted for rotation-within the chamber and adjacent the bottom thereofto cooperate with means formed on the carrier for engaging the threadsof the screw for positive driving movement of the carrier in response torotation of the screw in each of two opposite directions so as toadvance the carrier between advanced and retracted positions within thecarrier. According to a preferred embodiment, means have fur ther beenprovided for oscillating the rotation of the screw to continuously movethe carrier back and forth in the chamber over a relatively shortdistance whereby the parts of the apparatus will be kept from stickingor adhering together.

In general, it is an object of the invention to provide an improvedmeans for handling a carrier within a gas treatment chamber so as toprevent adhesion of the parts therebetween.

It is another object of the invention to provide an improvedsemiconductor element carrier for use within a gas treatment chamber.

It is yet another object of the invention to provide means forpositively and readily moving a carrier of the kind described betweenadvanced and retracted positions within a gas diffusion tube and tooscillate the longitudinal movement of the carrier within the tubeduring periods of treatment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view withportions broken away of an improved system according to the inventionand including schematic block diagram controls for operating same;

FIG. 2 is an enlarged detail view in perspective schematically showingan improved carrier unit according to the invention;

FIG. 3 is a side elevation section view taken in the region 33 of FIG.1;

FIG. 4 is an enlarged detail view of an elementsupporting portion of thecarrier shown in FIG. 2 and taken in the region of 4-4 thereof;

FIG. 5 is a transverse section view in enlarged detail taken along theline 55 of FIG. 1;

FIG. 6 is a diagrammatic representation showing three stages in thesequence of operation of the apparatus shown in FIG. 1;

FIG. 7 is an enlarged detail view of a terminal convolution of the leadscrew shown inn the apparatus in FIG. 1',

FIG. 8 is a perspective view of the exterior of a diffusion furnaceconstruction utilizing the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In general, as shown inFIG. 8, a diffusion furnace 10 includes a heating chamber 11 and anumber of diffusion tube assemblies 12 disposed to extend through theheating chamber 11. At the rear of furnace 10, a control cabinet 13houses controls and apparatus for operating the diffusion tube assembly12 as shown in greater detail in FIG. 1 and FIG. 3.

Tube assembly 12 comprises an elongated, generally cylindrical, tubularchamber 14 of heat resistant, pure material, such as quartz, wherebyhigh temperatures can be created within the confines of furnace 10without generating impurities to contaminate the elements being treated.Tube assembly 12 is disposed to extend outwardly of the front and rearwalls l6, l7 respectively which are constructed of suitable material,such as stainless steel or the like. Immediately behind and spaced fromfront wall 16, a secondary wall 18, also of stainless steel, serves toprovide a flue 19 into which gases exhausting from within chamber 14 canbe drawn.

Thus, means have been provided for passing gas into and out of chamber14 as by means of the elongated flow passage connection 21 for admittinggas, such as boron, for diffusion treatment of the elements 33 thereinwhile a flow passage 23 discharges gas into flue 19 via the gasconnection 24.

The outer end of chamber 14 is normally covered by a cylindrical closureelement 26 which serves to seal the end of chamber 14 and therebyprevent introduction of contamination by gases or otherwise into theinterior of chamber 14.

The protruding end of chamber 14 provides a cooling zone 27 into whichelements 33 can be withdrawn while supported on a moving elongatedcarrier 28, as shown more particularly in FIG. 2. Carrier 28 isconstructed of heat resistant material, such as quartz, so as topreclude emission of contaminants during treatment of elements 33.

Carrier 28 includes elongated, parallel side portions 29 for engagingand riding upon the sloping inner surface portions of chamber 14 (FIG.By virtue of the fact that the cross-section of chamber 14 iscylindrical in shape, and that the side portions 29 resting upon theinterior surface of chamber 14 lie in a common plane, carrier 28 will besupported to ride in a substantially horizontal plane.

Carrier 28 further includes element-supporting portions disposed betweenside portions 29, such as the transversely extending members 31.

Each member 31 is formed with a number oflaterally spaced slots 32,having a relatively flat bottom thereto, for receiving a semiconductorwafer element 33 of generally circular configuration but formed with achord segment portion removed so as to fit snugly upon the flat bottomof the slot 32. The plane of elements 33 are oriented, accordingly, inthe direction of the passage of gas through the interior of chamber 14so as not to create turbulent flow in the gas as it passes thereacross.

Carrier 28 is further prepared with a retrieving handle 34 located atthe outer end of carrier 28 (when it is positioned within chamber 14) sothat by means of a hook or other device carrier 28 can be engaged andwithdrawn from within the cooling zone 27 of chamber 14.

Finally, each end of carrier 28 includes screw follower means in theform of an arcuate planar element 36, 37 disposed at an angle to thedirection of travel of carrier 28. 7

Thus, an elongated lead screw element 38 also formed of quartz isdisposed in chamber 14 adjacent the bottom thereof and mounted forrotation in a stationary position aligned to engage the thread-engagingelements 36, 37 so as to positively drive carrier 28 back and forthwithin chamber 14.

Thus, lead screw 38 includes a threaded portion flanked by elongatedunthreaded portions 38a, 38b (FIG. 6). Lead screw 38 is journalled atits right hand end as viewed in FIG. 1 simply by urging its conical tipinto a comically-shaped depression formed in a stationary journal block41 also of quartz. Journal block 41 is formed as a portion of theinterior of chamber 14 at a distance removed from the access opening 42of chamber 14 whereby carrier 28 will be advanced by lead screw 38outwardly into zone 27.

The other end of lead screw 38 is supported for rotation by means of theannular Teflon support bushings 43 (FIG. 3) carried about the left endof lead screw element 38 captured in a groove 44 formed therearound.Lead screw element 38 is rotated by a drive connection as now to bedescribed with respect to FIG. 3.

A resilient generally cylindrical rotary seal 46, formed with outwardlybiased rims 46a, 46b, rotates within the interior surface of chamberextension portion 140 to maintain a seal therewith. The end of leadscrew element 38 fits into a drilled hole formed axially of seal 46 andby means of a notch 47 and Rulon pin 48 extending transversely throughthe body of seal 46 forms a positive drive connection between therotating seal 46 and the shaft portion of lead screw element 38.

Means for rotating seal 46 comprises a flexible drive cable 49 carryinga standard attaching head 51 whereby a set screw 52 can be tighteneddown against the flat 53 formed on the outer end of a drive shaft 54.Drive shaft 54 is formed with a flange portion 540 through which drivepins 56 serve to couple drive shaft 54 with seal 46.

Drive shaft 54 is supported by means of an annular stainless steelretaining ring 57 and an annularly shaped lock spring 58 lodged in agroove formed about the interior of the end of chamber extension portion14a.

Accordingly, by rotation of cable 49, lead screw element 38 can be madeto rotate in one direction or the other as desired and, accordingly,means have been provided for rotating lead screw element 38 in each oftwo opposite directions in a stepwise mode of operation.

Thus, a four-phase or other suitable stepping motor 61 is coupled by apinion 62 and a positive displacement drive belt 63 to drive a bull gear64 about is axis of rotation. At its axis of rotation, there has beenattached a head 66 of a type comparable to head 51 and in this mannerrotation of lead screw 38 is obtained.

The system as disclosed in FIG. 1 provides a means for oscillating therotation of lead screw 38 to continuously cycle carrier 28 back andforth within chamber 14 over a relatively short distance only sufficientto keep the parts of the apparatus from sticking.

Accordingly, a square wave generator or oscillator 67 of conventionalconstruction feeds a train of pulses at a selected rate along line 68into a stepper/driver circuit 69 operatively coupled electrically toactivate stepping motor 61. A phase-reversing circuit 71 provides one orthe other of two outputs 72, 73 by suitable means, such as the bi-stablestates of a series of flipflops whereby, with a four-phase operatedstepping motor 61, for example, the phases can be activated in a forwardor reverse sequence simply by sequencing the flip-flop elements inconventional style to start from one direction or the other.

Further, phase-reversing circuit 71 automatically reverses the sequenceof signals appearing on lines 72, 73 after relatively short numbers ofpulses have been provided on these lines whereby stepping motor 61 willnormally oscillate between forward and reverse modes of operation tooscillate the rotation of lead screw 38.

In addition, as shown in FIG. 1 schematically, pushbuttons labeled L"and R have been provided in conventional style to establish and hold oneor the other of the two output conditions on lines 72, 73 for drivingmotor 61 in one or the other of its two directions.

In operation (FIG. 6), carrier 28, pre-loaded with a number ofsemiconductor wafer elements 33 located in slots 32, is disposed intochamber 14 with threadfollower element 36 positioned to pass overjournal block 41, the unthreaded portion 381:, and into engagement withthe first of threads of lead screw 38. Subsequently, closure 26 isapplied to the access opening 42 for sealing the outer end of tubeassembly 12. Depressing push-button L of phase-reversing circuit 71serves to maintain a predetermined state on line 72 or 73 so as to causestepping motor 61 to advance carrier 28 leftwardly into the heating zone74 within furnace 10. Ultimately, thread-follower element 36 will reachthe left end of the threaded portion of lead screw 38 and continue outonto the unthreaded portion 38b by virtue of the face that by this timethread-follower element 37 will have engaged the threaded portion oflead screw element 38 and be driving carrier 28.

Ultimately, as thread-follower element 37 reaches the leftmostconvolution of the threaded portion of lead screw 38, carrier 28 will bearrested by the last remaining convolution or thread and come to a stopwhile leaving thread-follower element 37 in threaded engagement with thethreaded portion of lead screw Thus, the terminal convolutions of thethreaded portion of lead screw 38 at each end thereof has been formed toarrest and retain a follower 36, 37 so as to prevent carrier 28 frombecoming disengaged in the furnace or at the right hand end. Thus, theterminal convolutions include an abrupt termination 76 thereof wherebydriving engagement between the screw convolutions and screw-followerelements 36, 37 will be terminated before carrier 28 advances beyond theend of the threaded portion of lead screw element 38.

Accordingly, by driving carrier 28 from either end, only a limitedportion of lead screw element 38 is required to be formed with a thread.This is advantageous since the formation of threads around a quartz rodis a relatively expensive undertaking but is required under thecircumstances in order to obtain a quartz construction within thediffusion tube.

Reverse feeding of carrier 28 operates in the same manner whereby theterminal convolution on the right hand end of the threaded portion ofscrew 38 will fail to disengage element 36 driving the end of carrier 28and, accordingly, carrier 28 is never out of reach of the threadedportion of lead screw 38, while carrier 28 can be positively positionedsubstantially beyond either end of the threaded portion.

As thus described, it will be readily evident that there has beenprovided an improved impurity treatment furnace characterized by animproved gas treatment chamber assembly whereby the semiconductorcarrier or boat" is positively driven between advanced and retractedpositions within the assembly and while within the heating zone 74 willbe oscillated continuously longitudinally back and forth within arelatively short distance so as to preclude bonding or adherence ofcarrier 28 to the interior-of chamber 14 or sticking of the variousparts of the rotationally driven lead screw assembly.

I claim: I

1. In a treatment furnace for preparing semiconductor elements inexposure to gases and having an elongated chamber carried by the furnaceto receive said elements via one end thereof, said one end protrudingfrom a wall of the furnace, means for passing gases into and out of saidchamber for treatment of said elements, means forming a carrier tosupport a number of said elements therefrom for movement in saidchamber, an elongated screw mounted for rotation within, and adjacent tothe bottom of, said chamber, means formed on said carrier for engagingthe threads of said screw for positive movement of said carrier inresponse to rotation of said screw, and motive means for rotating saidscrew to positively drive said carrier between advanced and retractedpositions within said chamber.

2. In a treatment furnace having an elongated chamber for preparingsemiconductor elements, a carrier within the chamber for supporting saidelements for treatment, an elongated screw mounted for rotation withinsaid chamber, means disposed at each end of said carrier for engagingsaid screw in positive driving relation to advance and retract saidcarrier in response to rotation of said screw, means for passing gasinto and out of said chamber for treatment of said elements, and meansfor rotating said screw in each of two opposite directions to drive saidcarrier.

3. In a furnace according to claim 2 wherein the last named meansfurther includes means for oscillating the rotation of said screw tocontinuously cycle said carrier to move back and forth in said chamberover a relatively short distance sufficient to keep the parts of theapparatus from sticking.

4. In an impurity treatment chamber of a type having means for passinggases into and out of same, a carrier movable longitudinally thereof andadapted to support semiconductor elements in said chamber, said carrierincluding side portions for engaging the inner surface of said chamberand supporting said carrier in a substantially horizontal plane,element-supporting portions carried between said side portions,threadengaging means carried from the ends of said carrier, and anelongated lead screw element disposed in said chamber and mounted forrotation in position aligned to engage said thread-engaging means topositively drive said carrier back and forth within said chamber.

5. In a chamber according to claim 4 wherein said lead screw elementincludes unthreaded elongated end portions at each end and a threadedportion therebetween, said threaded portion having a followerarrestingconvolution at each end serving to preclude unscrewing the terminal oneof said thread-engaging means thereby retaining said carrier threadedlyengaged thereon at both ends of its travel along said lead screwelement.

6. A carrier for supporting elements for treatment within an impuritytreatment chamber, said carrier comprising a pair of spaced apart sideportions adapted to ride upon the inner surface of the chamber, meansbetween said side portions for supporting a number of semiconductorelements to be treated, and threadfollower means disposed from the lastnamed means in position for engaging an elongated threaded elementmounted for rotation within the chamber.

7. In a treatment furnace having an elongated chamber for preparingsemiconductor elements, a carrier within the chamber for supporting saidelements for treatment, an elongate drive element in said chamber, meansdisposed at each end of said carrier for engagingsaid drive element inpositive driving relation to advance and retract said carrier inresponse to driving of said elongate element, means for passing gas intoand out of said chamber for treatment of said semiconductor elements,and means for driving said drive element in each of two oppositedirections to drive said carrier, the last named means further includingmeans for oscillating the movement of said drive element to continuouslycycle said carrier to move back and forth in said chamber over arelatively short distance sufficient to keep the parts of the apparatusfrom sticking while maintaining said carrier substantially at apredetermined station in said chamber during said oscillating

1. In a treatment furnace for preparing semiconductor elements inexposure to gases and having an elongated chamber carried by the furnaceto receive said elements via one end thereof, said one end protrudingfrom a wall of the furnace, means for passing gases into and out of saidchamber for treatment of said elements, means forming a carrier tosupport a number of said elements therefrom for movement in saidchamber, an elongated screw mounted for rotation within, and adjacent tothe bottom of, said chamber, means formed on said carrier for engagingthe threads of said screw for positive movement of said carrier inresponse to rotation of said screw, and motive means for rotating saidscrew to positively drive said carrier between advanced and retractedpositions within said chamber.
 2. In a treatment furnace having anelongated chamber for preparing semiconductor elements, a carrier withinthe chamber for supporting said elements for treatment, an elongatedscrew mounted for rotation within said chamber, means disposed at eachend of said carrier for engaging said screw in positive driving relationto advance and retract said carrier in response to rotation of saidscrew, means for passing gas into and out of said chamber for treatmentof said elements, and means for rotating said screw in each of twoopposite directions to drive said carrier.
 3. In a furnace according toclaim 2 wherein the last named means further includes means foroscillating the rotation of said screw to continuously cycle saidcarrier to move back and forth in said chamber over a relatively shortdistance sufficient to keep the parts of the apparatus from sticking. 4.In an impurity treatment chamber of a type having means for passinggases into and out of same, a carrier movable longitudinally thereof andadapted to support semiconductor elements in said chamber, said carrierincluding side portions for engaging the inner surface of said chamberand supporting said carrier in a substantially horizontal plane,element-supporting portions carried between said side portions,thread-engaging means carried from the ends of said carrier, and anelongated lead screw element disposed in said chamber and mounted forrotation in position aligned to engage said thread-engaging means topositively drive said carrier back and forth within said chamber.
 5. Ina chamber according to claim 4 wherein said lead screw element includesunthreaded elongated end portions at each end and a threaded portiontherebetween, said threaded portion having a follower-arrestingconvolution at each end serving to preclude unscrewing the terminal oneof said thread-engaging means thereby retaining said carrier threadedlyengaged thereon at both ends of its travel along said lead screwelement.
 6. A carrier for supporting elements for treatment within animpurity treatment chamber, saiD carrier comprising a pair of spacedapart side portions adapted to ride upon the inner surface of thechamber, means between said side portions for supporting a number ofsemiconductor elements to be treated, and thread-follower means disposedfrom the last named means in position for engaging an elongated threadedelement mounted for rotation within the chamber.
 7. In a treatmentfurnace having an elongated chamber for preparing semiconductorelements, a carrier within the chamber for supporting said elements fortreatment, an elongate drive element in said chamber, means disposed ateach end of said carrier for engaging said drive element in positivedriving relation to advance and retract said carrier in response todriving of said elongate element, means for passing gas into and out ofsaid chamber for treatment of said semiconductor elements, and means fordriving said drive element in each of two opposite directions to drivesaid carrier, the last named means further including means foroscillating the movement of said drive element to continuously cyclesaid carrier to move back and forth in said chamber over a relativelyshort distance sufficient to keep the parts of the apparatus fromsticking while maintaining said carrier substantially at a predeterminedstation in said chamber during said oscillating movement.